There are many assets above ground and below ground that need to be protected and avoided. Included in these assets are utility lines and components and protected areas, such as archeological sites and habitat of endangered species. There are millions of miles of utility lines around the world, some buried and some above ground. These utility lines include, without limitation, electric power lines, telephone lines, water lines, sewer lines, fiber-optic cable lines, natural gas transmission lines, natural gas distribution lines, and utility lines for transporting hazardous liquids.
Every year incidents occur in which mobile ground breaking equipment comes in contact with utility lines with costly results in loss of life and/or loss of money. Statistics kept by the United States Office of Pipeline Safety regarding pipelines indicate that between 1986 and 2001 there were 1286 incidents involving natural gas transmission lines, which killed 58 people, injured 217 people and caused 284 billion dollars in property damage. In that same period there were 2159 incidents involving natural gas distribution lines, which killed 282 people, injured 1264 people and caused 256 billion dollars in property damage. There were also 3034 incidents involving utility lines carrying hazardous liquids which killed 36 people, injured 244 people and caused a further 731 billion dollars in property damage. In order to understand the full impact of such incidents, one would have to also include environmental damage and economic loss as a result of a service disruption.
There have been many attempts to address damage prevention when groundbreaking equipment is used around utilities and other assets that need protection. Non-exhaustive examples of these attempts include marking the location of a utility by painted lines. Commonly in the past, the utility companies and/or service companies are called to the site to place marks (spray the ground with an identifying color; for example, red for electric lines, yellow for gas lines and so forth) on the surface to show the location of a specific utility line and/or its components. Such marking is not permanent and typically lasts only for the one earth moving operation, such as digging a trench, for which the utilities were marked.
Another approach was to make a record of the location of the utility lines as the line was placed in the earth. However, the accuracy of the location is dictated by the accuracy of the reference point. It has been found that attempting to locate a utility line based op this record has resulted in an error of up to 15 feet or more because of the inaccuracy in the position of the reference point.
Another approach is to use the record of the location of a facility, with its inherent error from inaccurate reference points, as the record to compare to the location of a piece of ground breaking equipment. This approach is disclosed in U.S. Pat. No. 6,282,477 issued on Aug. 28, 2001 to Adam J. Gudat, et al., the disclosure of which is hereby incorporated by reference herein. As noted in the Gudat et al patent at Col. 5, lines 39-50, there is a region of uncertainty that is a function of at least one parameter, including, but not limited to, inherent errors in the position determining system and errors in the determined location of the object (utility).
The determined location of the utility may be acquired by underground imaging, which is commonly accomplished by the use of ground penetrating radar. Examples of underground imaging are set forth in U.S. Pat. No. 6,766,253 issued Jul. 20, 2004; U.S. Pat. No. 6,735,888 issued May 18, 2004; U.S. Pat. No. 6,700,526 issued Mar. 2, 2004; and U.S. Pat. No. 6,388,629 issued May 14, 2004, the disclosure of each of which is hereby incorporated by reference herein.
A common way of referencing the generated data identifying location of the utility is to use a fixed object, such as the curbing of a road. An example of the use of ground penetrating radar to acquire location data for underground utilities is described in U.S. Pat. No. 6,751,553, the disclosure of which is hereby incorporated by reference herein.